1. Field of the Invention
This invention relates generally to radio frequency power devices and more particularly to tuning assemblies for oscillating the frequency output of such devices. More specifically, the subject invention relates to a novel tuning assembly for oscillating the frequency of an electromagnetic field generated within a hermetically sealed device, and in particular within a magnetron tube, to thereby oscillate the frequency output of such device.
2. Description of the Prior Art
Radio frequency power devices are well known in the art. Such power devices may generate radio frequency outputs at a fixed frequency or at variable frequencies oscillating within a specified operating frequency band. In general, such radio frequency power devices include therewithin a hermetically sealed housing which is either evacuated, as in the case of a vacuum tube or a magnetron, or is filled with an inert gas. A variety of well known systems are utilized to generate an electromagnetic field within the hermetic housing, with the current induced from such an electromagnetic field being directed to an output antenna.
One commonly used arrangement for generating such an electromagnetic field includes positioning an anode ring about a centrally disposed cathode within the hermetic housing, and then establishing a magnetic field around the anode. This is commonly done by positioning a pair of magnets on either side of the anode. In this manner, an electrical field is created between the cathode and anode, and a magnetic field is generated within the interaction space between the cathode and anode, thereby establishing an electromagnetic field at the anode. In this particular arrangement, the anode ring defines a cavity space radially inwardly thereof wherein the frequency of the electromagnetic field is established. In other arrangements, such as in a coaxial magnetron tube, the cavity space wherein the frequency of the electromagnetic field is defined may be located exterior to the anode.
In the above described arrangement, the frequency of the electromagnetic field is defined by the physical size and shape of the cavity as well as the conductive properties of the material utilized to form the cavity. One known cavity arrangement includes a plurality of tabs or vanes projecting radially inwardly from the inner surface of the anode ring, and the frequency of the electromagnetic field is determined by the conductive properties of the vanes, the size of the vanes, the spacing between the vanes, and the manner in which the vanes may be electrically interconnected at their radially inner edges. Thus, by adjusting these variables of the vane structure and thereby changing the overall volume of the cavity, any desired frequency may be pre-selected prior to construction of the radio frequency device. The manner in which the vane structure is constructed and altered so as to establish a desired fixed frequency is well known in the art and will not be discussed in any detail herein.
Once the shape and the volume of the frequency determining cavity is established, the frequency of the electromagnetic field generated within such a device is set, and the resultant frequency output of the device becomes fixed. In variable frequency power devices, however, the frequency of the electromagnetic field within the hermetic housing is tunable or varied in an oscillating manner by changing the volume of the frequency determining cavity in an oscillatory fashion, thereby changing the inductive properties thereof. One known technique for changing the volume of the frequency determining cavity includes positioning an electrically conductive member within the cavity and oscillating that member therewithin, thereby varying the volume of the cavity in an oscillatory manner. To achieve such oscillatory motion of an electrically conductive member within the cavity, prior devices have commonly utilized mechanical arrangements for moving the electrically conductive member.
One such mechanical tuning arrangement utilizes a thin wall bellows or diaphragm as part of the hermetic housing. The electrically conductive members are then mechanically connected to such a bellows or diaphragm, and the bellows or diaphragm are mechanically oscillated by a motor located outside the hermetic housing.
Another known tuning arrangement for changing the volume of the frequency determining cavity includes positioning electrically conductive members within the cavity and rotating such members along the inner surface of the anode ring. Such rotation is effected by magnetically coupling the rotating electrically conductive member to an electromagnetic power source disposed outside the housing. A distinct disadvantage to this latter technique, however, is that by rotating an electrically conductive member within the frequency determining cavity, the electromagnetic field frequency can be varied, but not in an oscillatory manner.
The movable bellows or diaphram arrangement described above, however, also has certain disadvantages. One major disadvantage with this mechanical tuning arrangement is that the walls of the bellows or diaphragm must be relatively thin to effect such movement and are thereby subject to mechanical fatigue and failure. If such a bellows or diaphragm does fail, the vacuum or inert gas environment within the hermetic housing is destroyed, and the power source thereby becomes useless. Another disadvantage is that since the bellows or diaphragm must be constructed from a thin walled material, atmospheric gas can penetrate such thin material over a period of time and can thereby affect the internal environment. Therefore, such mechanical arrangements have a relatively short storage or shelf life.
A further disadvantage of the above mechanical tuning assemblies is that a significant energy input is required to operate such assemblies. This requirement is due to the mechanical resistance offered by the bellows or diaphragm arrangement as well as to the atmospheric dampening effect on the mechanical parts located exterior to the hermetic housing or envelope.
The novel tuning assembly of the present invention, however, overcomes the disadvantages of known mechanical tuning assemblies, and provides a relatively simple yet efficient means for oscillating the frequency of the electromagnetic field generated within such radio frequency power sources.